Treatment of spinal metastases

ABSTRACT

A radiotherapy system, and preferably a brachytherapy system, for delivering radiation to tissue surrounding an interstitial space is provided. While the system can be used for a variety of purposes, the system is preferably used to treat spinal metastases. In general, the system includes a catheter member having a proximal end, a distal end, and an inner lumen extending therethrough, and a structural support adapted to fit within an interstitial space in load bearing portion of a patient&#39;s body and having an internal space for removably receiving the distal end of the catheter member. At least one anchoring element can be disposed proximate to the distal end of the catheter. The anchoring element is preferably adapted to fit within the internal space in the structural support so as to anchor the distal end of the catheter therein. The system further includes a radiation source disposable within the internal space of the structural support through the lumen in the catheter for delivering radiation to tissue surrounding the interstitial space.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/269,555, filed on Oct. 11, 2002 and entitled “Treatment of SpinalMetastases,” now U.S. Pat. No. 6,695,760 B1.

FIELD OF THE INVENTION

The invention relates generally to apparatus for use in treatingproliferative tissue disorders, and more particularly to an apparatusfor the treatment of such disorders in the body by the application ofradiation.

BACKGROUND OF THE INVENTION

Malignant tumors are often treated by surgical resection of the tumor toremove as much of the tumor as possible. Infiltration of the tumor cellsinto normal tissue surrounding the tumor, however, can limit thetherapeutic value of surgical resection because the infiltration can bedifficult or impossible to treat surgically. Radiation therapy can beused to supplement surgical resection by targeting the residual tumormargin after resection, with the goal of reducing its size orstabilizing it. Radiation therapy, or surgical excision followed byradiation therapy, is commonly used to treat spinal metastases.Metastases are tumors that have grown in a location that is remote fromthe site that the tumor started, and spinal metastases result from thespread of cancer cells into a patient's vertebral column.

Radiation therapy can be administered through one of several methods, ora combination of methods, including external-beam radiation,stereotactic radiosurgery, and permanent or temporary interstitialbrachytherapy. The term “brachytherapy,” as used herein, refers toradiation therapy delivered by a spatially confined radioactive materialinserted into the body at or near a tumor or other proliferative tissuedisease site. Owing to the proximity of the radiation source,brachytherapy offers the advantage of delivering a more localized doseto the target tissue region.

For example, brachytherapy is performed by implanting radiation sourcesdirectly into the tissue to be treated. Brachytherapy is mostappropriate where 1) malignant tumor regrowth occurs locally, within 2or 3 cm of the original boundary of the primary tumor site; 2) radiationtherapy is a proven treatment for controlling the growth of themalignant tumor; and 3) there is a radiation dose-response relationshipfor the malignant tumor, but the dose that can be given safely withconventional external beam radiotherapy is limited by the tolerance ofnormal tissue. In brachytherapy, radiation doses are highest in closeproximity to the radiotherapeutic source, providing a high tumor dosewhile sparing surrounding normal tissue. Interstitial brachytherapy isuseful for treating malignant brain and breast tumors, among others.

While devices exist for delivering radiation to treat metastases, thereis still a need for instruments which can be used to providebrachytherapy to target tissue within a load bearing portion of a humanbody, such as within a patient's spine.

SUMMARY OF THE INVENTION

The present invention generally provides a brachytherapy system fortreating metastases within a load bearing portion of a patient's body.The system includes a structural support having an internal space andbeing adapted to fit within an interstitial space within a load bearingportion of a patient's body, and a catheter member having proximal anddistal ends and at least one lumen extending therebetween. Thestructural support is preferably configured to fit within a resectedcavity in a patient's bone, and more particularly in a patient's spine.At least one anchoring element is disposed proximate to the distal endof the catheter and is adapted to fit within the internal space in thestructural support so as to anchor the distal end of the cathetertherein. The system also includes a radiation source disposable withinthe internal space through the at least one lumen in the catheter fordelivering radiation to the tissue surrounding the interstitial space.

The system can be adapted to control the distribution of radiation totissue surrounding the interstitial space. In one embodiment, a shieldcan be formed on a portion of at least one of the structural support andthe anchoring element for shielding radiation sensitive tissue from aportion of the radiation. Alternatively, or in addition, a portion ofthe structural support adapted to be positioned adjacent to a patient'sspine or other vital organs and structures can be formed from aradio-opaque material adapted to shield the patient's spinal cord fromradiation. In yet another embodiment, the radiation source can beconfigured to provide an asymmetric radiation dose within the tissuesurrounding the interstitial space so that radiation sensitive tissuesurrounding the interstitial space receives a lesser dose. In otheraspects, the anchoring element can be an outer expandable member, andthe system can include an inner expandable member disposable within theouter expandable member and effective to removably receive the radiationsource. Preferably, the outer expandable member is adapted to bepositioned substantially adjacent to tissue surrounding the interstitialspace when expanded, and the inner expandable member is effective toposition the radiation source at a predetermined distance apart from theouter expandable member to provide a minimum absorbed dose fordelivering radiation to tissue adjacent the outer expandable member. Inanother embodiment, at least one of the outer expandable member and theinner expandable member can be partially coated with a radio-opaquematerial effective to shield radiation sensitive tissue from a portionof the radiation source. Alternatively, or in addition, a shieldeffective to shield radiation sensitive tissue from a portion of theradiation source can be disposed between the outer expandable member andthe inner expandable member.

In another embodiment of the present invention, a brachytherapy systemfor delivering radioactive emissions to an interstitial space in aresected vertebral body is provided. The system includes a cage memberadapted to fit within an interstitial space in a resected vertebral bodyand having an internal space, a catheter body having proximal and distalends, and a first expandable balloon member disposed adjacent the distalend of the catheter body and defining an inner spatial volume having aradiation source disposed therein. The first expandable balloon memberis adapted to be disposed within the internal space in the cage member.

In other aspects of the present invention, a method for treating spinalmetastases is provided. The method includes the steps of surgicallyresecting a vertebral body to create an interstitial space, providing aninterstitial brachytherapy apparatus for delivering radioactiveemissions, intraoperatively placing the interstitial brachytherapyapparatus into the interstitial space, providing a controlled dose ofradiation to tissue surrounding the apparatus, and removing theinterstitial brachytherapy apparatus. The apparatus preferably includesa catheter member having proximal and distal ends and at least onelumen, at least one anchoring element disposed proximate to the distalend of the catheter and adapted to anchor the distal end of the catheterwithin the interstitial space, and a radiation source disposable withinthe internal space through the at least one lumen in the catheter fordelivering radiation to the tissue surrounding the interstitial space.The step of surgically resecting a vertebral body can further includethe step of providing a structural support adapted to fit within theinterstitial space, and positioning the structural support in theinterstitial space, wherein the interstitial brachytherapy apparatus ispositioned in an internal space within the structural support. Theradiation source is preferably placed into the interstitialbrachytherapy apparatus after placement of the apparatus into theinternal space in the structural support, and is preferably removed fromthe internal space in the structural support before removal of theapparatus.

DESCRIPTION OF THE DRAWINGS

The foregoing features, objects and advantages of the invention willbecome apparent to those skilled in the art from the following detaileddescription of a preferred embodiment, especially when considered inconjunction with the accompanying drawings in which:

FIG. 1 is perspective view illustration of a brachytherapy system fortreating spinal metastases in a resected vertebrae;

FIG. 2 is a perspective view illustration of one embodiment of astructural support member for use with the system of the presentinvention;

FIG. 3 is a diagram illustrating one embodiment of a catheter member foruse with the system of the present invention;

FIG. 4A is a cross-sectional view of the catheter member shown in FIG. 3taken across line A—A;

FIG. 4B is a diagram illustrating another embodiment of a cathetermember for use with the system of the present invention having aradio-opaque coating disposed thereon for shielding radiation sensitivetissue; and

FIG. 5 is a side view of an interstitial brachytherapy apparatus fordelivering asymmetric radioactive doses to body tissue.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention generally provides a radiotherapy system, andpreferably a brachytherapy system, for delivering radiation to tissueand/or bone surrounding an interstitial space. While the system can beused for a variety of purposes, the system is preferably used to treatspinal metastases. In general, the system 10 (FIG. 1) includes acatheter member 12 having a proximal end 14, a distal end 16, and aninner lumen 18 (FIG. 3) extending therethrough, and a structural support20 adapted to fit within an interstitial space 22 in load bearingportion of a patient's body and having an internal space 24 forremovably receiving the distal end 16 of the catheter member 12. Atleast one anchoring element 46 can be disposed proximate to the distalend 16 of the catheter 12. The anchoring element 46 is preferablyadapted to fit within the internal space 24 in the structural support 20so as to anchor the distal end 16 of the catheter 12 therein. The system10 further includes a radiation source (not shown) disposable within theinternal space 24 of the structural support 20 through the lumen 18 inthe catheter 12 for delivering radiation to tissue surrounding theinterstitial space 22.

The structural support 20 used with the system 10 of the presentinvention can have a variety of configurations, but is preferably acage-like member adapted to fit within a resected vertebrae 50 and toreceive a load bearing portion of the vertebrae 50. The support 20 canhave any shape and size, but should include an internal space 24 formedtherein for receiving the distal end 16 of the catheter member 12. In anexemplary embodiment, the structural support 20 is a spinal fusion cage.FIG. 2 illustrates one example of a suitable structural support 20 foruse with the system 10 of the present invention. The illustrated supportis the BP® Cage manufactured by Sulzer Spine-Tech and described in U.S.Pat. Nos. 5,015,247, 5,484,437 and 5,741,253. Other suitable supportsfor use with the system of the present invention include, for example,the Ray TFC® manufactured by Surgical Dynamics Inc. and described inU.S. Pat. Nos. 5,015,247, 5,484,437, and 5,741,253, and the Infuses BoneGraft and the LT-CAGE® manufactured by Medtronic Sofamor Danek. A personhaving ordinary skill in the art will appreciate that a variety ofstructural supports can be used, and that the support can include avariety of features not shown or described herein.

As shown in FIG. 2, the BP Cage 20 has a generally elongate, cylindricalshape and includes an internal space 24 formed therein. The cage 20includes superior and inferior surfaces 26, 28, first and secondtransverse sides 30, 32 extending between the superior and inferiorsurfaces 26, 28, and proximal and distal ends 34, 36. An inner lumen,which forms the internal space 24, extends between the proximal end 34and the distal end 36 of the cage 20 along a longitudinal axis L. Theproximal end 34 of the cage 20 is open for receiving the distal end 16of the catheter 12. The distal end 36 is also open, but can be solid toprevent over-insertion of the catheter 20 and/or to shieldradiation-sensitive tissue from radiation, as will be discussed in moredetail below. The cage 20 further includes one or more openings 44extending through each of the transverse sides 30, 32 for receivingbone-growth promoting materials. The openings 44 can also bestrategically placed to control the direction of radiation delivered tothe tissue surrounding the interstitial space, as will also be discussedin more detail below. The cage 20 can also be adapted to mate with aninsertion tool (not shown). For example, the superior and inferiorsurfaces 26, 28 of the cage 20 can include one or more grooves 38, 40formed therein for receiving an insertion tool, and threads 42 disposedthere around for facilitating insertion of the cage 20 into aninterstitial space. In use, the cage 20 can be grasped by an insertiontool and rotated to thread the cage 20 into an interstitial space. Aperson having ordinary skill in the art will appreciate that a varietyof insertion tools and mating techniques can be used to position thecage in a resected cavity.

The catheter member 12 used with the system 10 of FIG. 1 can also have avariety of configurations, but is preferably a brachytherapy apparatusused to deliver radiation to tissue surrounding a resected cavity. Aperson having ordinary skill in the art will appreciate that virtuallyany brachytherapy apparatus can be used with the system 10 of thepresent invention. By way of non-limiting example, a suitablebrachytherapy apparatus for use with the system of the present inventionis disclosed in U.S. Pat. No. 6,413,204, issued Jul. 2, 2002, andentitled “Interstitial Brachytherapy Apparatus and Method for theTreatment of Proliferative Tissue Diseases,” which is herebyincorporated by reference herein.

FIG. 3 illustrates an exemplary embodiment of a catheter member 12 foruse with the system 10 of the present invention. As shown, the cathetermember 12 includes a proximal end 14, a distal end 16, and at least oneinner lumen 18 extending therebetween. The distal end 16 includes ananchoring element 46 disposed thereon for anchoring the distal end 16 ofthe catheter 12 within the internal space 24 of the cage member 20. Atleast one lumen 18 of the catheter 12 preferably includes a port 48 incommunication with the anchoring element 46 for expanding the anchoringelement 46. The anchoring element 46 can have virtually anyconfiguration, but is preferably an expandable balloon member, as shownin FIG. 3, that is primarily sealed around the port 48 on the distal end16 of the catheter member 12. In use, the expandable member 46 ismovable between a deflated position to allow insertion of the distal end16 of the catheter 12 into the internal space 24 in the support member20, and an inflated position, as shown, wherein air or fluid isdelivered through the lumen 18 and the port 48 in the catheter 12 toinflate the expandable member 46 and thereby anchor the distal end 16 ofthe catheter member 12 in the internal space 24 of the support 20. Theanchoring element 46 can have any shape and size, but preferably has apredetermined shape in its expanded form, as shown in FIG. 3, such that,when inflated, the anchoring element is adapted to securely fit withinthe internal space 24 of the structural support 20 to positively locatethe distal end 16 of the catheter 12 with respect to the cage 20 andwith the target tissue to be dosed with radiation. While the size of theanchoring element 46 can be predetermined, the size can be selectableduring treatment by inflating the anchoring element 46 to a desiredlevel. In an alternative embodiment (not shown), the anchoring element46 can be an expandable cage member, and the catheter 12 can optionallyinclude a control lever or similar mechanism for moving the expandablecage member between a contracted position and an expanded position. Aperson having ordinary skill in the art will appreciate that a varietyof anchoring elements can be used with the present invention.

The catheter 12 can also optionally include a second, inner expandablemember 52 disposed within the first, outer expandable member 46. Theinner expandable member 52 is also preferably an expandable balloonmember and is effective to receive a radiation source. The innerexpandable member 52 can have any shape and size, but is preferablyadapted to fit within the outer expandable member 46 and, when inflated,to be spaced a predetermined distance apart from the outer expandablemember 46. In use, the inner expandable member 52 is movable between adeflated position, in which the expandable member 52 is disposedadjacent the distal end of the catheter 16, and an inflated position, inwhich the inner expandable member 52 is disposed within, but spacedapart from, the outer expandable member 46. A second lumen 18 b, shownin FIG. 4A, and a second port 54 are provided on the catheter 12 forcommunicating with the inner expandable member 52.

With no limitation intended, the inner and outer expandable members 46,52 can be formed from a polymeric film wall, which may comprise abiocompatible, radiation resistant polymer. Suitable polymers include,for example, silastic rubbers, polyurethanes, polyethylene,polypropylene, polyester, and PVC.

The system 10 of the present invention is adapted to control thedistribution of radiation to tissue surrounding the interstitial space.One advantage to controlling the distribution of radiation to tissuesurrounding the interstitial space is that a minimum prescribed dose canbe delivered to the tissue in the target treatment region withoutover-exposing radiation-sensitive tissue, which can cause healthy tissuenecrosis.

In one embodiment, the structural support 20 can be adapted to allowradiation from a source within the cage to pass only to a desired regionof tissue. For example, where the system 10 is used to treat a spinalmetastases, the system 10 can be configured to provide less radiation inthe direction of the spinal cord. By way of non-limiting example, thesupport 20 can be formed from a radio-opaque material and can includeone or more radio-lucent regions for allowing radiation to betransmitted therethrough. Alternatively, the support 20 can be formedfrom a radio-lucent material and portions of the support can be coatedwith a radio-opaque shield effective to shield a desired region oftissue from radiation. The entire support 20 can also optionally beradio-lucent. Preferably, the distal end 36 of the support isradio-opaque to prevent radiation from coming into contact with apatient's spinal cord. In another embodiment, the support can be formedfrom a radio-opaque material and can include one or more openings,similar to the openings 44 illustrated in FIG. 2, that are effective toallow radiation to be delivered to a region of tissue positionedproximate to the openings.

In another embodiment, the anchoring element 46 and/or the innerexpandable member 52 can be adapted to control the distribution ofradiation to the tissue surrounding the interstitial space. For example,the inner expandable member 52 can be effective to receive a radiationsource and to position the radiation source a predetermined distanceapart from the outer expandable member 46, thereby providing a minimumabsorbed dose for delivering radiation to tissue adjacent the outerexpandable member 46. This configuration is described in more detail inU.S. Pat. No. 6,413,204, issued Jul. 2, 2002, and entitled “InterstitialBrachytherapy Apparatus and Method for Treatment of Proliferative TissueDiseases,” which is incorporated herein by reference. In general, theinner and outer expandable members have a volume that is configured toprovide an absorbed dose within a predetermined range throughout atarget tissue.

In another embodiment, at least one of the anchoring element 46 and/orthe inner expandable member 52 can be partially coated with aradio-opaque material effective to shield radiation sensitive tissuefrom a portion of the radiation source. By way of non-limiting example,FIG. 4B illustrates a radio-opaque material 62 coated onto a distalportion of the surface of the inner expandable member 52. The coating 62can be strategically positioned to shield radiation sensitive tissue,and/or to provide an asymmetric isodose curve as described in U.S.patent application Ser. No. 09/464,727, filed on Dec. 16, 1999, andentitled “Asymmetric Radiation Dosing Apparatus and Method,” which isincorporated herein by reference.

Radio-opaque materials suitable for coating onto an expandable surfaceinclude, for example, barium, tungsten, bismuth, tantalum, and tin. Asan alternative to coating the inner and/or outer expandable members 46,52 with a radio-opaque material, a radiation-blocking or absorbingshield (not shown) can be positioned between the anchoring element 46and the inner expandable member 52, or within the inner expandablemember 52 to produce a desired isodose curve. A person having ordinaryskill in the art will appreciate that other configurations may beemployed to achieve the desired isodose curves and/or shielding ofradiation sensitive tissue.

In yet another embodiment, the radiation source itself can be configuredto provide radiation to a desired region of tissue surrounding theinterstitial space. By way of non-limiting example, FIG. 5 illustratessystem 100 having a catheter 110 including first and second lumens (notshown) extending from first and second proximal ports 118, 120 in amolded hub 122. The first lumen is effective to carry a radioactivesource 124 and the second lumen communicates with inflation port 126formed through the side wall of the catheter member 110. The distal end128 of the catheter 110 includes an outer spatial volume 130 defined byan outer polymeric film barrier 132 that is appropriately spaced fromthe radioactive source 124. The outer volume 130 encompasses inflationport 126. The radiation source 124 comprises a wire 134 having one ormore solid radioactive particles 136 located thereon. The radioactivesource 124 can either be preloaded into the catheter 110 at the time ofmanufacture, or loaded into the device after it has been implanted intothe space formerly occupied by the excised tumor. If loaded afterimplantation, the solid radiation emitting material 136 can be insertedthrough the first lumen on a wire 134, for example, using an afterloader(not shown). Radiation source 124 has an asymmetric configuration withrespect to a longitudinal axis 138 of the instrument 110. That is,radiation source 124 is shaped so as to result in an isodose profile 140that varies radially about the longitudinal axis 138. More simply, theisodose profile 140 of FIG. 5 has a shorter radius from the longitudinalaxis 138 on the top side of the instrument 110 as shown in FIG. 5 thanon the bottom side. The asymmetrically shaped isodose curve 140 may becreated by providing a plurality of solid radioactive particles 136 on acurved wire 134 in a spaced apart relationship. This configuration willresult in certain of the solid radioactive particles 136 being fartherfrom the longitudinal axis 138 of the instrument 110 than others, andwill result in the illustrated asymmetric isodose profile 140. One wayto provide the illustrated radioactive source 124 configuration is toform wire 134 from a solid or tubular shape memory alloy such asnickel-titanium alloys known in the art to have such properties. Wire134 can then be preformed to the desired shape, can be compressed into asubstantially straight configuration to pass through the first lumen,and will resume its desired shape once inside volume 130 where wire 134will be free from steric constraints imposed inside the first lumen. Theresulting asymmetric isodose curve 140 can be further tailored by usingsolid radioactive particles 136 having differing specific activities toachieve the desired dosing. Such a configuration is also described inU.S. patent application Ser. No. 09/464,727, filed on Dec. 16, 1999, andentitled “Asymmetric Radiation Dosing Apparatus and Method.”

In use, the support member 20 is preferably positioned within a resectedcavity in a patient's body, preferably within an interstitial spacecreated in a resected vertebrae 50, as shown in FIG. 1. The distal end16 of the catheter member 12 is then anchored in the internal space 24in the support member 20 by inflating the anchoring element 46. Theanchoring element 46 can be inflated with air or other fluids, such assaline or a radiation absorbing fluid such as a contrast media used inangiography. The catheter 12 can be pre-loaded with a radioactivesource, or alternatively the radioactive source can be inserted into thecatheter 12 via lumen 18. The radioactive source dwells in the distalend 16 of the catheter 12, preferably in the inner expandable member 52,until the prescribed dose of radiotherapy is delivered, or theradioactive source can be inserted for prescribed amounts of time on adaily or other scheduled basis until the prescribed dosage has beenachieved. The radioactive source is then retrieved and the catheter 12is removed. The radiation treatment may end upon removal of thebrachytherapy apparatus 12, or the brachytherapy may be supplemented byfurther doses of radiation supplied externally.

Suitable radiation sources for use with the system of the presentinvention include both solids and liquids. By way of non-limitingexample, the radiation source can be a radionuclide, such as I-125,I-131, Yb-169, Ir-192 as a solid source, I-125 as a solid source, orother radionuclides that emit photons, beta particles, gamma radiation,or other therapeutic rays. The radioactive material can also be a fluidmade from any solution of radionuclide(s), e.g., a solution of I-125 orI-131, or a radioactive fluid can be produced using a slurry of asuitable fluid containing small particles of solid radionuclides, suchas Au-198, Y-90. Moreover, the radionuclide(s) can be embodied in a gel.One radioactive material useful in the invention is Iotrex™, a sterilesingle use, non-pyrogenic solution containing sodium3-(¹²⁵I)iodo-4-hydroxybenzenesulfonate (¹²⁵I-HBS), available fromProxima Therapeutics, Inc. of Alpharetta, Ga. Radioactive micro spheresof the type available from the 3M Company of St. Paul, Minn., may alsobe used. This radioactive source can either be preloaded into thecatheter at the time of manufacture or loaded into the device after ithas been implanted into the space formerly occupied by the excised tumorwith one or more solid radioactive micro spheres inserted through thecatheter on a wire, for example, using an afterloader (not shown).

A method according to the invention for treating spinal metastases andother malignancies begins by surgically resecting a vertebral body tocreate an interstitial space. Following tumor resection, but prior toclosing the surgical site, the surgeon intra-operatively places aninterstitial brachytherapy apparatus, having a catheter member with atleast one anchoring element as described above, into the interstitialspace in the resected cavity. A radiation source is then positionedwithin the internal space in the anchoring element through at least onelumen in the catheter for delivering a controlled dose of radiation tothe tissue surrounding the interstitial space. The brachytherapyapparatus is then removed. In a further embodiment, the step ofsurgically resecting a vertebral body can further include the step ofproviding a structural support adapted to fit within the interstitialspace, and positioning the structural support in the interstitial space.In this embodiment, the interstitial brachytherapy apparatus ispositioned in an internal space within the structural support. Theradiation source is preferably placed into the interstitialbrachytherapy apparatus after placement of the apparatus into theinternal space in the structural support, and is removed from theinternal space in the structural support before removal of theapparatus.

A person having ordinary skill in the art will appreciate that thebrachytherapy system of the present invention can have virtually anyconfiguration, and the embodiments illustrated and described herein areintended merely as exemplary embodiments and should not be construed tolimit the present invention. Moreover, it will be understood that theforegoing is only illustrative of the principles of the invention, andthat various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention. Allreferences cited herein are expressly incorporated by reference in theirentirety.

1. A system for treating metastases in a load bearing portion of apatient's body, comprising: a structural support adapted to fit within acavity in a patient's spine and to structurally stabilize the loadbearing portion, the structural support defining an internal space; aradiation source positionable within the internal space for deliveringradiation to tissue surrounding the cavity.
 2. The system of claim 1,further comprising a shield, the shield being adapted to shieldradiation sensitive tissue from a portion of the radiation.
 3. Thesystem of claim 1, wherein the structural support is configured to fitwithin a cavity in a patient's bone.
 4. The system of claim 1, wherein aportion of the structural support adapted to be positioned adjacent apatient's spine is formed from a radio-opaque material adapted to shieldthe patient's spinal cord from radiation.
 5. The system of claim 1,wherein the radiation source is configured to provide an asymmetricradiation dose within the tissue surrounding the cavity so thatradiation sensitive tissue surrounding the cavity receives a lesserdose.
 6. The system of claim 1, wherein the structural support and theradiation source are adapted so that the radiation source is positionedat a predetermined distance apart from tissue surrounding the cavity soas to provide a prescribed absorbed dose of radiation to the surroundingtissue to a predetermined depth.
 7. A method for treating metastases ina patient's spine, comprising: placing a structural support within aninterstitial space in the spine to provide structural support therein;placing a radiation source within the structural support; and providinga controlled dose of radiation to tissue surrounding the structuralsupport.
 8. The method of claim 7, further comprising surgicallyresecting a vertebral body to at least partially create an interstitialspace.
 9. The method of claim 7, wherein a radiation shield is provided,the shield being adapted to shield radiation sensitive tissue from aportion of the radiation.
 10. The method of claim 9, wherein a portionof the structural support is formed from a radio-opaque material adaptedto shield the patient's spinal cord from radiation.
 11. The method ofclaim 7, wherein the radiation source is configured to provide anasymmetric radiation dose within the tissue surrounding the interstitialspace so that radiation sensitive tissue surrounding the interstitialspace receives a lesser dose.
 12. The method of claim 7, wherein theradiation source is positioned so as to provide a prescribed absorbeddose of radiation to tissue surrounding the cavity to a predetermineddepth.
 13. The method of claim 7, wherein the radiation source comprisesat least one solid radiation source disposed on at least one elongatemember.
 14. The method of claim 7, wherein a plurality of solidradiation sources are disposed in a spaced apart relationship on asingle elongate member.